INFO: rcu detected stall in neigh_timer_handler (3)

Status: upstream: reported on 2026/08/07 01:39
Reported-by: syzbot+77594b6302d7010c94e4@syzkaller.appspotmail.com
First crash: 72d, last: 2d22h
▶ ▼ Similar bugs (29)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in neigh_timer_handler (6) netfilter 1 1 2139d 2139d 0/29 auto-closed as invalid on 2021/03/09 03:20
linux-6.6 INFO: rcu detected stall in neigh_timer_handler 1 1 228d 228d 0/2 auto-obsoleted due to no activity on 2026/06/12 03:02
linux-6.1 INFO: rcu detected stall in neigh_timer_handler (4) 1 1 3d10h 3d10h 0/3 upstream: reported on 2026/10/14 22:04
upstream INFO: rcu detected stall in neigh_timer_handler (8) net 1 syz, C done done 72 797d 857d 28/29 fixed on 2024/10/21 12:45
upstream INFO: rcu detected stall in neigh_timer_handler net 1 1 2885d 2885d 0/29 auto-closed as invalid on 2019/05/23 06:47
upstream INFO: rcu detected stall in neigh_timer_handler (2) net 1 2 2594d 2596d 13/29 fixed on 2019/10/09 10:54
upstream INFO: rcu detected stall in neigh_timer_handler (4) net 1 1 2509d 2509d 0/29 closed as invalid on 2019/12/04 14:04
linux-5.15 INFO: rcu detected stall in neigh_timer_handler 1 1 398d 398d 0/3 auto-obsoleted due to no activity on 2025/12/23 11:36
upstream INFO: rcu detected stall in neigh_timer_handler (5) net 1 1 2241d 2241d 0/29 auto-closed as invalid on 2020/11/26 10:25
linux-6.6 INFO: rcu detected stall in neigh_timer_handler (2) 1 1 84d 84d 0/2 upstream: reported on 2026/07/25 18:11
linux-5.15 INFO: rcu detected stall in neigh_timer_handler (2) 1 2 235d 237d 0/3 auto-obsoleted due to no activity on 2026/06/04 18:05
upstream INFO: rcu detected stall in neigh_timer_handler (3) net 1 2 2514d 2514d 0/29 closed as invalid on 2019/11/29 14:24
linux-6.1 INFO: rcu detected stall in neigh_timer_handler (3) 1 1 368d 368d 0/3 auto-obsoleted due to no activity on 2026/01/23 04:30
upstream INFO: rcu detected stall in neigh_timer_handler (7) net 1 1 2014d 2014d 0/29 auto-closed as invalid on 2021/07/11 19:14
linux-6.1 INFO: rcu detected stall in neigh_timer_handler (2) 1 1 622d 622d 0/3 auto-obsoleted due to no activity on 2025/05/14 07:23
linux-4.14 INFO: rcu detected stall in neigh_timer_handler 1 5 2359d 2479d 0/1 auto-closed as invalid on 2020/08/30 16:21
linux-6.1 INFO: rcu detected stall in neigh_timer_handler 1 4 753d 863d 0/3 auto-obsoleted due to no activity on 2025/01/03 05:12
upstream BUG: soft lockup in neigh_timer_handler (2) net 1 2 633d 663d 0/29 closed as invalid on 2025/02/28 15:46
upstream BUG: soft lockup in neigh_timer_handler (4) perf 1 1 203d 203d 0/29 closed as invalid on 2026/05/19 12:17
android-5-10 BUG: soft lockup in neigh_timer_handler (2) 1 1 21d 21d 0/2 premoderation: reported on 2026/09/26 09:04
android-5-10 BUG: soft lockup in neigh_timer_handler 1 2 1151d 1159d 0/2 auto-obsoleted due to no activity on 2023/11/22 05:43
linux-4.19 BUG: soft lockup in neigh_timer_handler 1 4 1436d 1694d 0/1 auto-obsoleted due to no activity on 2023/03/12 06:57
android-54 BUG: soft lockup in neigh_timer_handler (2) 1 5 521d 606d 0/2 auto-obsoleted due to no activity on 2025/08/13 05:16
linux-4.14 BUG: soft lockup in neigh_timer_handler 1 3 1704d 1747d 0/1 auto-closed as invalid on 2022/06/16 21:59
android-5-15 BUG: soft lockup in neigh_timer_handler 1 1 99d 99d 0/2 auto-obsoleted due to no activity on 2026/10/08 13:26
upstream BUG: soft lockup in neigh_timer_handler (3) batman 1 2 532d 533d 0/29 auto-obsoleted due to no activity on 2025/08/01 18:42
android-6-1 BUG: soft lockup in neigh_timer_handler 1 2 1065d 1087d 0/2 auto-obsoleted due to no activity on 2024/02/16 02:11
android-54 BUG: soft lockup in neigh_timer_handler 1 3 849d 861d 0/2 auto-obsoleted due to no activity on 2024/09/18 13:19
upstream BUG: soft lockup in neigh_timer_handler net 1 1 1183d 1157d 0/29 auto-obsoleted due to no activity on 2023/10/20 21:15

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-...!: (1 GPs behind) idle=739/1/0x4000000000000002 softirq=19728/19737 fqs=19 
	(detected by 1, t=10504 jiffies, g=26625, q=186)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4280 Comm: kworker/0:5 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Workqueue: events_power_efficient neigh_periodic_work
RIP: 0010:variable_test_bit arch/x86/include/asm/bitops.h:214 [inline]
RIP: 0010:test_bit include/asm-generic/bitops/instrumented-non-atomic.h:135 [inline]
RIP: 0010:cpumask_test_cpu include/linux/cpumask.h:344 [inline]
RIP: 0010:cpu_online include/linux/cpumask.h:895 [inline]
RIP: 0010:trace_irq_enable_rcuidle+0x6a/0x180 include/trace/events/preemptirq.h:40
Code: 00 00 e8 69 d3 f9 ff 45 89 fc 41 c1 ef 06 4a 8d 3c fd 28 28 6b 8e be 08 00 00 00 e8 e0 19 3f 00 31 f6 4c 0f a3 25 0e d8 eb 0c <40> 0f 92 c5 40 0f 92 c6 bf 02 00 00 00 e8 94 d5 f9 ff 40 84 ed 0f
RSP: 0018:ffffc9000311f958 EFLAGS: 00000047
RAX: ffffffff817f4f01 RBX: 0000000000000000 RCX: ffffffff817f5010
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8e6b2828
RBP: 0000000000000000 R08: ffffffff8e6b282f R09: 1ffffffff1cd6505
R10: dffffc0000000000 R11: fffffbfff1cd6506 R12: 0000000000000000
R13: 0000000000000000 R14: ffffffff89e00e46 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000001 CR3: 000000004942d000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000200000000300 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <TASK>
 trace_hardirqs_on+0x57/0x80 kernel/trace/trace_preemptirq.c:44
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x7f/0x4a0 kernel/rcu/tree_plugin.h:674
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 82 fc 9c 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc9000311fa40 EFLAGS: 00000206
RAX: 803ef5ae0755b100 RBX: 1ffff92000623f4c RCX: 803ef5ae0755b100
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a4c00
RBP: ffffc9000311fb18 R08: ffffffff910150ff R09: 1ffffffff2202a1f
R10: dffffc0000000000 R11: fffffbfff2202a20 R12: ffffffff8d123400
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 __neigh_notify+0x282/0x2e0 net/core/neighbour.c:3395
 neigh_cleanup_and_release+0x9d/0x250 net/core/neighbour.c:101
 neigh_periodic_work+0x406/0xc70 net/core/neighbour.c:947
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10414 jiffies! g26625 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=1 timer-softirq=14017
rcu: rcu_preempt kthread starved for 10415 jiffies! g26625 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:I stack:27632 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
 rcu_gp_fqs_loop+0x2be/0x11f0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
 rcu_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487
 print_other_cpu_stall+0x1110/0x1270 kernel/rcu/tree_stall.h:592
 check_cpu_stall kernel/rcu/tree_stall.h:745 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x845/0x1120 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:2021
 tick_sched_handle kernel/time/tick-sched.c:254 [inline]
 tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4b0/0xb60 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x397/0x8b0 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
 __sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0x4d/0xc0 arch/x86/kernel/apic/apic.c:1108
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:queued_write_lock_slowpath+0x129/0x270 kernel/locking/qrwlock.c:78
Code: f0 41 81 0e 00 01 00 00 43 0f b6 04 27 84 c0 74 37 44 89 f1 80 e1 07 80 c1 03 38 c1 7c 2a 4c 89 f7 e8 0b 08 60 00 eb 20 f3 90 <43> 0f b6 04 27 84 c0 74 15 44 89 f1 80 e1 07 80 c1 03 38 c1 7c 08
RSP: 0018:ffffc90000dd0360 EFLAGS: 00000206
RAX: 00000000000001ff RBX: ffffc90000dd03b0 RCX: ffffffff815e601f
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff8e34d098
RBP: ffffc90000dd0410 R08: ffffffff8e34d09b R09: 1ffffffff1c69a13
R10: dffffc0000000000 R11: fffffbfff1c69a14 R12: dffffc0000000000
R13: 1ffff920001ba070 R14: ffffffff8e34d098 R15: 1ffffffff1c69a13
 queued_write_lock include/asm-generic/qrwlock.h:97 [inline]
 do_raw_write_lock+0x1e6/0x260 kernel/locking/spinlock_debug.c:210
 ___neigh_create+0xdf3/0x2210 net/core/neighbour.c:625
 ip6_finish_output2+0xacc/0x1640 net/ipv6/ip6_output.c:129
 dst_output include/net/dst.h:452 [inline]
 NF_HOOK include/linux/netfilter.h:302 [inline]
 ndisc_send_skb+0xb7c/0x1410 net/ipv6/ndisc.c:513
 ndisc_send_ns+0x662/0x860 net/ipv6/ndisc.c:655
 ndisc_solicit+0x300/0x4f0 net/ipv6/ndisc.c:747
 neigh_probe net/core/neighbour.c:1017 [inline]
 neigh_timer_handler+0xaa9/0xff0 net/core/neighbour.c:1099
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1699 [inline]
 __run_timers+0x56c/0x810 kernel/time/timer.c:1970
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
 handle_softirqs+0x336/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:default_idle+0xb/0x10 arch/x86/kernel/process.c:730
Code: b7 48 89 df e8 76 fc f2 f7 eb ad e8 6f aa f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 00 cc 66 90 0f 00 2d f7 61 5a 00 fb f4 <c3> 0f 1f 40 00 41 57 41 56 53 49 be 00 00 00 00 00 fc ff df 65 48
RSP: 0018:ffffc90000d67d48 EFLAGS: 000002c2
RAX: 20da713067448400 RBX: ffff88813fe48000 RCX: 20da713067448400
RDX: 0000000000000001 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a4c00
RBP: ffffc90000d67e80 R08: ffff8880b8f3b30b R09: 1ffff110171e7661
R10: dffffc0000000000 R11: ffffed10171e7662 R12: 1ffff920001acfb4
R13: dffffc0000000000 R14: 1ffff11027fc9000 R15: 0000000000000000
 default_idle_call+0x81/0xc0 kernel/sched/idle.c:112
 cpuidle_idle_call kernel/sched/idle.c:202 [inline]
 do_idle+0x3a1/0x650 kernel/sched/idle.c:326
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:424
 start_secondary+0x32f/0x430 arch/x86/kernel/smpboot.c:281
 secondary_startup_64_no_verify+0xb1/0xbb
 </TASK>

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/15 09:55 linux-5.15.y a051a4bf909f 8fb0ae89 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in neigh_timer_handler
2026/09/18 20:37 linux-5.15.y 0248c33e835e 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in neigh_timer_handler
2026/09/12 16:19 linux-5.15.y 0996e0926f6b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in neigh_timer_handler
2026/08/22 15:45 linux-5.15.y 0eb903b5b519 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in neigh_timer_handler
2026/08/07 01:38 linux-5.15.y 9c7634c60784 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in neigh_timer_handler
* Struck through repros no longer work on HEAD.